Electromechanical transducers



April 11, 1967 A. F. MOSTARDO, JR., ET Al.

ELECTROMECHANICAL TRANSDUCERS Filed July 29, 1963 United States Patent3,313,892 ELECTROMECHANICAL TRANSDUCERS August F. Mostarrlo, In,Norridge, and Floyd W. Cross, Wheaton, lll., assignors to IndustrialResearch Products,

Inc., Franklin Park, 111, a corporation of Delaware Filed July 29, 1963,Ser. No. 298,332 6 Claims. (Cl. 179-115) The present invention relatesto transducers, and more particularly to miniature. transducers of thetype shown in copending US. patent application Ser. No. 27,006, filedMay 5, 1960, by Elmer V. Carlson.

In both the present invention and in the Carlson invention, there isprovided an E-shaped armature in which the outer arms of the E are heldfixedly within a magnetic stack. The magnetic stack includes twopermanent magnets spaced apart with their opposite poles confronting oneanother across a gap area. At the outer arms of the armature,non-magnetic spacers are fitted on either side of the armature armsbetween the magnets to secure the outer armature arms in place. Thesespacers end a short distance inwardly of the outer arms leaving a gap oneither side of the intermediate arm of the armature in the space betweenthe opposed pole faces. This gap is called the working gap and theintermediate armature arm is vibratable within this gap, as will beexplained more fully.

To complete the magnetic circuit between the permanent magnets, thearmature and magnetic stack are fitted in a rectangular magnetic casewith the lower of the magnets directly resting on and engaging thebottom wall of the case. Above the magnetic stack, a magnetic bulkheadis fitted into the case and contacts the case side walls. In this way,the case and bulkhead complete the steady flux path of the fieldsgenerated by the permanent magnets.

The intermediate arm of the armature has positioned thereabout a signalcoil whose generated magnetic field is completed through the armature.This field path may be traced from the armature intermediate arm throughthe base or spine of the armature to the outer armature arms and finallythrough individual magnetic pole pieces in the magnetic stack internallyof the permanent magnets.

A drive pin extends normally from a connection to the intermediate orvibratable armature arm through an opening in the upper magneticbulkhead to a connection to a diaphragm. The diaphragm is mountedparallel to the bulkhead and spaced therefrom. When the transducer isused as a microphone, the diaphragm is positioned to vibrate in responseto sound waves impinging against it. As the diaphragm vibrates, it inturn vibrates the intermediate armature arm. The arm, on vibration, ismoved successively adjacent the permanent magnet poles to change themagnetic potential of the armature. This change in the armature magneticpotential generates a corresponding varying voltage in the coil, thecoil voltage variations being transmitted from the coil to the externalcircuit.

In use as a receiver, changes in voltage are fed to the coil. These coilchanges generate a varying flux field which acts on the armaturevibratable arm and which in turn vibrates the diaphragm to efiect anacoustic output.

Miniature transducers of the type described are known from the Carlsonapplication, and are of particular advantage in hearing aids andespecially in hearing aids fitted into spectacle and behind-the-earframes. In these hearing aids, the tendency has been to develop smallerand yet smaller transducers for making the hearing aids less bulky andless noticeable. With these size reductions, the quality of receptionmust not be diminished. In addition, this industry is highlycompetitive, leading to extensive research into designs of minimal size,ease and minimum assembly cost without lessening the quality of thefinished transducer.

It is, therefore, an object of the invention to provide an improvedminiature transducer which may be assembled readily and inexpensively.

It is a further object of the invention to provide an improvedtransducer construction which is more compact than prior transducers andutilizes its compact size to effect a high quality transducer output.

To effect these and other objects, the present invention utilizes themagnetic stack structure, bulkhead, and E- armature shown by Carlson.The armature of Carlson is modified by bending the connecting base orspine of the armature to a position normal to the armature arms andextending parallel to the magnetic stack structure. The bulkhead ofCarlson is modified to allow this E- armature with flange to movewithout interference. At the corners adjacent the armature base, thebulkhead has extensions designed to fit the magnetic structure andarmature tightly within the enclosing case or envelope. The bulkheadalso has an opening through which a drive pin extends for joining thearmature vibratable arm to the diaphragm.

The diaphragm member is constructed with an outer frame disposed to fittightly within the case side walls. The frame may be laminated or slitto contain an ovalshaped layer of plastic within its sheet members, andthis plastic has affixed at the center thereof a diaphragm of aluminumor the like. The completed diaphragm member is essentially contained ina plane with a peripheral mounting or spacing flange at its edges, asheretofore used in Knowles Patent No. 3,002,058, Sept. 26, 1961. In thediaphragm plane, the plastic oval acts as a hinge about the entire edgeof the diaphragm allowing the diaphragm to vibrate in a direction normalto the diaphragm plane.

To complete the assembly, a housing cover is fitted over the diaphragmto enclose the transducer within the case. The housing cover has acentrally positioned sound opening spaced above the diaphragm. Thishousing cover butts against the top of the case side wall and iscemented or otherwise adhered in place, as are many of the internalcomponents of the transducer.

The invention both as to its organization and principle of operation,together with further objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawings in which:

FIGURE 1 is an exploded view of a transducer of the present invention;

FIGURE 2 is a perspective view of the transducer of FIGURE 1 with theouter case and other components broken away in part to show the interiorconstruction;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2; and,

FIGURE 4 is a perspective view of the armature as used herein.

Turning to the drawings in detail, there is shown the transducerinternal assembly 10 within an enclosing housing including a bottom case12 and a housing cover 14. The internal assembly 10 includes themagnetic stack structure 15, the armature 16, the signal coil 18, and

the diaphragm member 20.

The magnetic structure includes a sandwich-like stack which includesrespectively a bar permanent magnet 24 extending transversely across thestructure. Above the magnet and coextensive therewith is a lower polepiece 26 of magnetically permeable material. Above the pole piece 26,adjacent both ends thereof, are fitted spacers 28 of non-magneticmaterial. These end spacers are mounted above the pole piece 26 and areused to rest thereon the outside arms and 32 of the E-shaped armature16. These outer arms are mounted on the spacers, and there is a secondpair of like spacers 34 mounted permanently above each of the armatureouter arms. Above the upper spacers 34 is positioned a second transversepole piece 36 coextensive with the lower pole piece 26 and lower magnet24. A final member of the stack 15 is a second permanent bar magnet 38which is magnetized transversely as is the lower magnet 24. The stack issecured as a single unit by suitable adhesives, rivets, or the like.

The magnets, as mentioned previously, are magnetized transversely sothat the upper surface 40 of the lower magnet 24 may present a singlepole such as a north pole. Assuming a north pole for the upper surface49 of the lower magnet 24, the confronting or bottom face of magnet 38would be a south pole (the pole opposed to that at surface 40).

The armature 16, as mentioned, is E-shaped, and has its outer arms 30and 32 secured in the magnetic stack 15 and has its intermediate arm 42extending through the stack in a working gap 44 provided by the absenceof spacers in the mid-transverse stack portion. By this construction,the magnetic stack extends vertically and transversely with the armature16 cantilevered therefrom at the midlevel height of the stack.

About the vibratable armature arm 42 between the stack and the base orspine of the armature, there is mounted a signal coil 18. This coil isconnected by suitable leads 52 through openings 53 in the magnetic caseto a source of power. The coil 18, when energized, generates a magneticfield which is concentrated in strength through its axis. The armaturevibratable arm 42 extends through the coil 18 along the coil axis in theat-rest condition, and serves to complete the field generated by thecoil through the armature.

Secured to the top surface of upper magnet 38 by suitable means is thebulkhead 54 which is made of magnetic material, and is of widthsufficient to fit tightly Within case 12. This bulkhead may also besuitably connected to the exterior of coil 18 by the use of adhesives.The bulkhead is cantilevered from its connection to the magnetic stackand extends in superimposed spaced relationship parallel to the armaturearms. At the corners most remote from its connection to the magneticstack, the bulkhead 54 terminates in two parallel, spaced-apart tips 56which are designed to abut against the adjacent wall of case 12 and holdthe magnetic structure tightly within the case. Between these tips, thebulkhead includes a cutout 60 which uncovers a portion of the vibratablearm 42. The cutout 60 adjacent its innermost end passes therethroughdrive pin 62 which connects the vibratable arm 42 to the diaphragm 2%).Drive pin 62 is secured by any suitable method such as welding oradhesion to the vibratable arm. The drive pin extends through the cutout60 for connection by suitable method to the diaphragm. At the cutout end64, remote from the stack, the cutout is sufficiently wide to allow thearmature spine 50 to move easily without being impeded.

At the end remote from the stack, the armature arms 30, 32 and 42 arejoined by the armature spine 59 (back surface of the armature E) whichis bent to form substantially a right angle with the plane of thearmature arms 30, 32 and 42. This base or spine 50 extends upwardlywithin the area of cutout 66 at the end 64 inwardly of bulkhead tips 56.This armature bend 66 serves a number of purposes. First, to a limiteddegree, it stitfens the armature structurally and by this bend impedessome of the tendency of the outer arms 36 and 32 to vibrate. Thisvibration inhibition aids in setting the vibrational node of theintermediate arm 42 adjacent the bend 66 in the armature spine 50. Thissetting of the armature vibrational node results in a greater efliciencyfor the unit in that the vibrational forces imparted to the vibratablearm are utilized to a greater degree in causing motion of the armatureintermediate arm alone. In addition, this amature bend 66 lessens thelinear length of the case allowing a more compact, and generally smallerstructure than has been possible heretofore. Where the armature spineextends in the same plane as the armature arms, space must be left aboveand below the spine to allow free armature movement, this space addingbut little to the efficiency of the unit. By bending the arma ture spinenormal to the armature arms, this space is cut to a minimum allowing aneven shorter transducer case to be used.

The diaphragm member 20 includes a rectangular frame 70 sized to fittightly Within the case side walls. The frame has a flange '72 which isoffset in configuration to space the diaphragm member from the bulkhead54. The diaphragm frame rests on the bulkhead 54 in assembly to assurethe proper alignment of the member in the case. The diaphragm frame hasan oval layer 74 of plastic affixed to it inwardly of flange 72.Inwardly of this open plastic layer area called the surround 74, thereis afiixed to the plastic an oval-shaped diaphragm 76 of aluminum or thelike. This diaphragm is oval in shape, and light in weight so that it isallowed a limited amount of movement in a plane normal to the diaphragmmember plane by the compliance of plastic surround 74. At its center,the diaphragm 76 is afiixed to the drive pin 62 for movement therewith.By this construction, the diaphragm member 2%) is fabricated as anintegral unit substantially planar and including a support frame 70 withits flange '72, the complaint rnovernent-allowing-surround '74 and theactual diaphragm '76 in the center.

An inertance tube 80 is affixed to the internal assembly adjacent themagnetic stack and outwardly thereof. This tube 84) is L-shaped with ahorizontal section 82 paralleling the lower magnet 24 and adjacentthereto. The tube bends to a vertical section 84 which extends through asuitable circular opening %6 in one corner of the diaphragm frame 70 toterminate slightly above the diaphragm. The functioning of an inertancetube is Well known and will not be explained fully herein.

To complete the assembly, a lid or housing cover 14, the bottom edge ofwhich butts against the top edge of case 12, encloses the assembly 19.The lid may be cemented or otherwise adhered to the case to unite thestructure in an assembly Which cannot readily be disassembled to tinkerwith the interior. The case itself includes suitable small openings forthe coil leads, and an adjusting port adjacent the back end of onearmature outer arm to allow adjustment of the armature. In addition, thelid 14 has a single, small, circular opening 94 at its center to allowsound to enter the sound cavity between the lid 14 and the diaphgram 76.

To provide improved performance characteristics, the base or spine 50 ofthe armature may be secured relative to the case by an optional bracket96 extending from the armature spine St to a connection to the base.This bracket would be a stepped rigid bracket 96 firmly connected byadhesive or welding to both the armature spine 5t) and case 12. The useof such a bracket would further reduce the tendency of the armaturespine 50 to vibrate with the armature vibratable arm 42. Clearly withsuch a bracket in use, the vibrational node of the armature would beslightly past the rear end of the coil adjacent to the armature spine.Instead of being mounted on the case, the bracket may be mounted on thebulkhead 54 or the coil 18.

The ramifications or alternative relative sizes of the magnets and thespacers is set out clearly in the previously cited Carlson applicationand need not be repeated herein.

As in the cited Carlson application, the signal flux or field generatedby coil 18 is completed through the armature 16 and the pole pieces 26and 3-6, wholly within the internal assembly. The steady flux circuitgenerated by the permanent magnets is completed through the stackstructure, and magnetic case 12, and the upper bulkhead 54. Asmentioned, the magnets 24 and 38 are respectively in contact with thecase 12 and bulkhead 54 to complete the magnetic path. In this way, thesignal flux circuit and steady flux circuit are isolated from oneanother with the steady fiux circuit by its use of the case and bulkheadsurrounding the signal flux circuit. The steady flux circuitmagnetically shields the internal assembly from stray magnetic fields.Any such stray magnetic fields which are received by the case will in noway afiect the operation of the armature vibratable arm and the signalflux circuit of which it is a part.

The use of the upper bulkhead 54 is manifold. First, it serves thepurpose of completing the steady flux circuit about the coil andarmature. Further, its shape allows the drive pin to pass freelythere-through for connection to the diaphragm. Its shape furtherprovides or allows movement of the armature with its angled spine orflange 50 without interference. head act to space and fit the internalassembly tightly within the case. Also, the bulkhead serves as a solidmember on which the diaphragm frame may be rested. The constructionshown allows for ready assembly with the component parts sized andshaped to fit snugly within the case and abutting against the adjoiningcomponents.

While there has been shown what is at present thought to be a preferredembodiment of the invention, it may be understood that manymodifications may be made therein, and it is intended to cover in theappended claims all modifications which fall within the true spirit andscope of the invention.

What is claimed is:

1. In that type of electromagnetic transducer wherein the three ends ofthe arms of an E-shaped armature are positioned between spaced poles ofopposite polarity of a steady flux circuit, the plane of the base of theE-shaped armature lying normal to the plane of the three arms, and acase surrounding the operable parts with one wall lying parallel to theplane of the base of the E-shaped armature.

2. An E-shaped armature for use in a transducer comprising a flat plateof flux-permeable, flexible material having the plan configuration of anE, with all three arms of the E flexible at right angles to the fiatsurface of the flat plate, and with the base of the E positioned atright angles to the fiat surface of the plate.

3. An electromagnetic transducer comprising a steady flux circuitincluding spaced permanent magnets confronting one another with theopposite poles of the magnets opposing one another, an armature having aplurality of arms in a plane extending into the space between saidmagnets, one or more of the arms of said armature affixed in the spacebetween said magnets and another of said arms vibratable in the spacebetween the magnets, a back end of said armature connecting said arms,said armature back end forming substantially a right angle with theplane of the armature arms, a signal fiux circuit including saidarmature, and a magnetic case for completing the steady flux circuit andenveloping said signal flux circuit, with one wall of said case closelyadjacent the back end of said armature.

4. An electromagnetic transducer comprising a steady flux circuitincluding two spaced permanent magnets with their opposite polesconfronting across the space therebetween, an E-shaped armaturepositioned with its arms extending between the magnets of said circuit,a central arm of said armature vibratable in the steady flux circuit,

The corner tips 56 of the bulkouter arms of said armature afiixed in thespace between the magnets in the same plane as said central armaturearm, the portion of said armature connecting said arms comprising astiffening spine for said armature arms, said spine substantiallyforming a right angle with the plane of said armature, a signal fluxcircuit including said armature arms and completed therethrough, amagnetic case enveloping said steady flux circuit, said case in magneticengagement with said permanent magnets to complete said steady fluxcircuit from said magnets wherein said signal flux circuit is isolatedfrom the steady flux circuit.

5. An electromagnetic transducer comprising a magnetic stack includingspaced permanent bar magnets extending transversely of said transducer,said magnets confronting one another with opposite poles confrontingacross the space therebetween, an armature with a plurality of armsextending in the space between said magnets, means aflixing one or moreof said arms in said stack, another of said armature arms extendingbetween said magnets and vibratable therebetween, the back of saidarmature connecting said arms together, said armature back formingsubstantially a right angle with the plane of said arms, a coilsurrounding said vibratable arm, said armature arms and back comprisinga path for signal flux from said coil, a magnetic case enclosing saidstack and in contact with the lower of said magnets, a magnetic bulkheadmounted on the upper of said magnets and engaging said upper magnet,said bulkhead contacting said case walls whereby to complete a steadyflux circuit from said magnets through said case and said bulkhead toisolate said signal flux circuit therein.

6. An electroacoustic transducer comprising a magnetic stack includingspaced permanent bar magnets extending transversely of said transducer,said magnets confronting one another with opposite poles confrontingacross the space therebetween, an armature with a plurality of armsextending in the space between said magnets, means afiixing one or moreof said arms in said stack, another of said armature arms extendingbetween said magnets and vibratable therebetween, the back of saidarmature connecting said arms together, said armature back formingsubstantially a right angle with the plane of said arms, a coilsurrounding said vibratable arm, said armature comprising a path forsignal flux from said coil, a magnetic case enclosing said stack and incontact with a lower of said magnets, a bulkhead mounted on the upper ofsaid magnets and engaging said upper magnet, said bulkhead contactingsaid case walls whereby to complete a steady flux circuit from saidmagnets through said case and said bulkhead to isolate said signal fiuxcircuit therein, a diaphragm, a drive pin extending through saidbulkhead, said drive pin connecting said diaphragm to said armaturevibratable arm for movement therewith, a diaphragm frame, a compliantmember joining said diaphragm to said frame to position said diaphragmcentrally within said case, and a cover butted against said case tofully enclose said transducer.

References Cited by the Examiner UNITED STATES PATENTS 3,076,062 1/1963Fener 179-114 3,111,563 11/1963 Carlson 179-114 KATHLEEN H. CLAFFY,Primary Examiner.

F. N. CARTEN, A MCGILL, Assistant Examiners,

2. AN E-SHAPED ARMATURE FOR USE IN A TRANSDUCER COMPRISING A FLAT PLATEOF FLUX-PERMEABLE, FLEXIBLE MATERIAL HAVING THE PLAN CONFIGURATION OF ANE, WITH ALL THREE ARMS OF THE E FLEXIBLE AT RIGHT ANGLES TO THE FLATSURFACE OF THE